DESCRIPTION: (Applicant's Abstract) The overall goal of our research is to define the function of cannabinoid receptors (CBR) on immune cells in human health and diseases such as AIDS. The goal of the current project, however, is more limited and will define the CBR phenotype of the major immune cell subsets and determine in a limited way the potential of these receptors to function in immunomodulation. Limited data currently suggest that CBR subtypes are expressed and functional on immune cells. However, these seminal findings must be confirmed and extended. In aim 1, we will define the expression pattern of CB1 and CB2 receptor mRNA in purified immune subsets of T cells, B cells, NK cells, and macrophages isolated from mouse spleen. To examine the relationship between cell activity and CBR mRNA expression, mRNA will be measured in either freshly isolated cells (basal activity) or in cells activated by mitogens. In aim 2, we will extend the aim 1 data by using radioligand binding studies and flow cytometry to probe for cannabinoid binding sites and receptor proteins on the surface of immune cell subsets under basal and stimulated conditions of cell activity. The studies in aims 1 and 2 will test the hypothesis that immune cell subsets have a distinct CB1/CB2 phenotype which is subject to change following cell activation. In aim 3, we will determine the potential of CBR to mediate cannabinoid-induced immunomodulation or normal immune homeostasis. This will be done by testing if CBR positive immune cells are modulated in a receptor selective manner using either cannabinoid agonists or antagonists. Mitogen-induced T cell, B cell, and NK cell proliferation and TNF production by macrophages will be analyzed in the presence of cannabinoid agonists and antagonists and the structure/activity relationship and agonist potencies will be determined and related to the CBR phenotype. Mitogen-induced immune cell responses will also be tested in the presence of CBR antagonists only to determine the involvement of the receptors in immune cell responses. Aim 3 experiments will test the hypothesis that CBR on immune cells mediate cannabinoid-induced immunomodulation as well as normal immune homeostasis. The experiments proposed in this application will increase our understanding of CBR immunobiology and the biology of the brain/immune axis, both of which are new and important issues in human health and disease. These studies will also shed light on the health consequences of marijuana use and on the potential use of CBR agonists and antagonists as immunomodulators and regulators of immunity and inflammation.